The present invention relates in general to a method and apparatus for making a storage battery paste for the plates of electric batteries and more particularly relates to such method and control apparatus which facilitate greatly the production of the proper mixture of materials to achieve desired physical and chemical properties of the resulting battery paste.
A lead oxide mixture conventionally is used as a storage battery paste for the plates of electric batteries. Briefly, the process of making the battery paste includes the initial mixing in a power mixer of selected quantities of dry lead oxide, water and sometimes additives to form a viscous mixture. Once the water and lead oxide mixture is thoroughly dispersed, a measured quantity of sulfuric acid is added to the viscous mixture to be dispersed therein, thereby gradually rendering the reaction mixture less viscous in consistency. As the acid increasingly reacts with the other materials of the mixture, the consistency of the mixture continues to decrease to a point of minimum viscosity and then increases therefrom to completion of the process.
During this process of making battery paste, the temperature of the mixture rises to a peak and thereafter falls gradually therefrom. The temperatures of the mixture are controlled so that the temperatures are permitted to rise to a desired high temperature to enable the reaction to take place in a satisfactory manner for a desired battery paste formulation. The control of the temperature of the mixture is achieved by circulating ambient air through the mixture, by using heat exchanging water jackets for the mixer and by controlling the speed of the acid addition. Also, the heat of the reaction and the ambient air passing through the mixer causes water to vaporize from the mixture, thereby cooling the mixture.
After the reaction and cooling of a batch of battery paste, if the quality and the quantity of all of the materials forming the battery paste mixture were within acceptable limits, then the physical and chemical properties of the final product will also be within acceptable limits. Two of these properties are specific gravity and viscosity. The value of the specific gravity of the final product is determined by conventional testing equipment. Similarly, in accordance with industry practices, viscosity of the final product is tested by measuring with a penetrometer the value of plasticity, which value is inversely proportional to and thus provides an indication of the viscosity of the battery paste mixture.
While the quality and the quantity of the materials forming the mixture can be ordinarily controlled within limits, the quantity of water in the final product is subject to variation. Since the viscosity of the final product is dependent upon its water content, the viscosity is also subject to variation from batch to batch. A larger than desired quantity of water in the final battery paste mixture causes it to have a consistency which exhibits a lower than desirable viscosity (high plasticity value); whereas, a smaller than desired quantity of water causes the final mixture to be too viscous (low plasticity value). Excessive variations in the water content in the final product are to a great extent due to temperature changes in the ambient conditions and due to granular size differences of the lead oxide.
During the day, ambient temperature changes are caused by normal temperature changes of the air and the water used for cooling purposes and of the materials to be used in the process. Also, the temperature of the mixer used in the process varies throughout the day. In this regard, after a few batches, the temperature of an empty mixer ordinarily stabilizes at a temperature which is a few degrees lower than the discharge temperature of the battery paste, but the temperature of the mixer changes when the mixer ceases to operate due to a malfunction of other equipment associated therewith, or other reasons, such as process adjustments.
The variations of water content in the final product resulting from ambient temperature changes can ordinarily be compensated for by admitting controllably "trim" water to the final product, either manually or automatically, until the viscosity is reduced to a desired value. For a disclosure of a certain automatic apparatus and methods for adding the trim water at the completion of a battery paste making process, reference may be made to U.S. Pat. No. 4,027,859.
However, excessive variations in final product water content can result when both ambient temperature changes as well as lead oxide granular size differences occur at the same time to compound the problem. Lead oxide granular size can vary greatly depending on the manufacturer, or on the oxidizing process, or both, even though the different oxides may be within close chemical tolerances. The differences in granular size cause varying amounts of process water to be evaporated during the mixing cycles of the process. For similar weights, coarse grains have less surface exposure than fine grains, and, therefore, when wetted and heated, especially when cooling air is passed over the mixture, varying amounts of water are evaporated.
If different size lead oxides from two different manufacturers are used in two different batches, both batches could have vastly different process water requirements. When a mixture of the two different size lead oxides is supplied to the same mixer, the process water requirements can vary during the transition from one oxide to the other. To further complicate the problem, some lead oxides from the same supplier vary from one extreme to another.
Therefore, adding the problem of the ambient temperature changes to the multiplicity of complications associated with the use of lead oxide, can result in the necessity of adding unwanted and unduly large quantities of trim water to the final product. Major water additions to the battery paste after the completion of the chemical reaction adversely affect the chemical quality of the finished product, which is costly to manufacture. The unwanted addition of trim water to the final product by either manual or automatic techniques causes a loss in time of both the process cycle time and the operator's time, thereby decreasing production capacity accordingly.